This specification relates to power controllers for sensing and controlling power during hot swaps.
A hot swap power controller facilitates the addition of electrical devices to a system without removing power from other electrical devices in the system. An example of the use of a hot swap power controller is in a server rack, where server devices may be added by inserting the server devices while other server devices in the server rack and on the same power bus remain powered. When the server device is coupled to the server rack, and thus to the power bus, the hot swap controller monitors the supply voltage and other conditions, such as current, and can control the power up of the server device so as to avoid transients, such as excessive inrush currents. Once the server device reaches a powered state that meets a threshold, the hot swap power controller generates a “power good” signal to indicate to the server processor (or other system components) that the server device is now operable.
If a hot swap controller is not used, the server device may introduce a considerable capacitive load to the power bus. Because the capacitive load may be uncharged, it may demand a large inrush current to charge. The large inrush current, in turn, reduces the power bus voltage, which may cause brownouts among other electronic devices powered by the power bus.
Additionally, decoupling capacitors are used to smooth the voltage on a power bus. Due to limited bandwidth, power supplies cannot respond to instantaneous current changes that a capacitive load may introduce. To compensate for the changes in current, decoupling capacitors are connected across the power bus, from the supply conductor to the return conductor. The decoupling capacitors add a fast charge storage near the load that provides charge to the load. Accordingly, the use of the decoupling capacitor reduces the transients in the power supply voltage resulting from changes in the load current.